The present invention relates to a battery pack constituted by arranging aligned adjacent each other a plurality of prismatic battery modules.
In a known prior art battery pack 21 constituted by arranging aligned adjacent each other a plurality of prismatic battery modules, as shown in FIG. 7, end plates 23 are arranged at both ends in the direction of adjacent arrangement of adjacently arranged battery modules 22, the pack being integrated by restraining the battery modules 22 by linking the two end plates 23, 23 by restraining straps 24. Also, in this battery pack 21, in order to effectively cool the adjacently arranged battery modules 22, a large number of dispersed projections which abut each other when these battery modules 22 are adjacently arranged project on the two lateral faces of battery modules 22, coolant passages being formed between the opposite side faces of battery modules 22 by means of these projections.
The restraining straps 24 are typically constructed of strip-shaped plates, a pair of these being arranged with suitable separation on the respective mutually opposite long side faces of battery pack 21, the plate faces being arranged along the long side faces and the two ends being fixed by rivets 25 to end plates 23.
Consideration has also been given to an arrangement as shown in FIG. 8 wherein one or a plurality of restraining straps 26 are arranged along the pair of mutually opposite short side faces of battery pack 21, both ends thereof being fixed by rivets to end plates 23, both lateral faces of each battery module 22 being arranged to be effectively cooled by passing coolant in the direction indicated by the white arrow i.e. in the direction passing through the long side faces of battery pack 21.
However, in the construction of the battery pack 21 shown in FIG. 7, when the battery modules 22 are cooled by passing coolant in the direction passing through the long side faces of battery pack 21, the restraining straps 24 present obstructions to the flow of coolant, so that the coolant is unable to flow satisfactorily in a region of a wide area where the restraining straps 24 are arranged, making it impossible to cool battery modules 22 evenly and producing a poor cooling effect; as a result, there is the problem that the output characteristic and life of battery modules 22 are adversely affected.
In the construction of the battery pack 21 shown in FIG. 8, although efficient cooling of the battery modules 22 can be achieved since coolant flows through the entire surface of the long side faces, when large loads caused by expansion or rise in internal pressure due to charging/discharging of battery modules 22 act, there is the problem that deformation occurs in the middle of end plates 23 due to the long span between restraining straps 26, 26.
Also, since both ends of the restraining straps 24, 26 are fixed to end plates 23 by means of rivets 25, when disassembling battery pack 21 for purposes of maintenance, it is necessary to cut rivets 25, risking damaging end plates 23 and/or restraining straps 24, 26. A further risk is that, since the compressive force acting on battery pack 21 is released all at once simultaneously with the cutting of rivets 25, fragments of rivets 25 may fly about and end plates 23 and/or restraining straps 24, 26 may spring up. Yet a further problem is that also when assembling battery pack 21 a separate restraining jig is required; this makes the operation difficult to perform by anyone other than the manufacturer of battery pack 21; also, insufficiency of the strength of the rivet joints is liable to occur and there is a risk of their breaking.
In view of the above, an object of the present invention is to provide a battery pack wherein the battery modules can be efficiently cooled, there is no risk of deformation of the end plates, assembly can be achieved with restraining straps of fully sufficient strength and assembly or removal can be performed without a special jig, so that assembly and maintenance can be performed easily and efficiently.
In a battery pack according to the present invention in which prismatic battery modules are arranged adjacently in a condition with coolant passages formed between the battery modules and with their side faces of largest area being arranged in superimposed manner, being integrated by tying end plates arranged at both ends in the direction of adjacent arrangement of the battery modules tightly together by restraining straps, a plurality of restraining straps are arranged at suitable intervals on the long side face of the battery pack and the restraining straps have a cross-sectional shape in which their dimension in the perpendicular direction with respect to the long side face of the battery pack is larger than their dimension in the parallel direction.
In this way, there is no risk of deformation of the end plates since the span between the restraining straps is short, since the plurality of restraining straps are arranged with suitable intervals on the long side face of the battery pack. Furthermore, since the battery modules are arranged to be cooled by passing coolant in the direction passing through the long side face and, even if a plurality of restraining bands are provided on the long side face, the cross-sectional dimension of the restraining bands is small in the direction impeding the flow of coolant, the battery modules can be effectively cooled, making it possible to improve the output characteristic and life of the battery modules.
Suitable the cross-sectional shape of the restraining straps is a shape in which a curved surface along the direction of flow of the coolant that passes through the coolant passages or a plane parallel to the direction of flow occupies most of the external surface. Specifically, the restraining straps consist of members of circular cross-section, plate faces at both ends thereof being provided with a mounting portion along the mounting face of the end plate. Or the restraining straps consist of strip of rectangular cross-sectional shape arranged with its long side perpendicular to the long side face of the battery pack, plate faces at both ends thereof being provided with a mounting portion along the mounting face of the end plate.
If coolant passages are formed in the end plates in the direction perpendicular to the long side face of the battery pack, the side faces of the battery modules adjacent the end plate can also be efficiently cooled, so the output characteristic and life of all of the battery modules constituting the battery pack can be improved.
In a battery pack according to the present invention in which prismatic battery modules are arranged adjacently with their side faces of largest area being adjacently arranged in superimposed manner, being integrated by tying end plates arranged at both ends in the direction of arrangement of the battery modules tightly together by restraining straps, at least one end of the restraining straps and a mounting portion of one end plate are provided with a screw mechanism arranged along the longitudinal direction of the restraining strap whereby the effective length of the restraining strap can be extended or diminished. By giving the screw mechanism a sufficient degree of strength, assembly of the restraining straps can be achieved with a fully sufficient degree of strength. Also, since assembly/removal of the restraining straps can be performed by operation of the screw mechanism without using a special jig, assembly and/or maintenance can be performed easily and efficiently.
Suitably, by providing a tightening bolt whereof the head is engaged with one end of the restraining strap or one end is fixed, by forming a bolt hole through which the tightening bolt passes in the end plate, and by engaging a nut threaded onto the tightening bolt with the side of the end plate opposite to the side that adjoins the battery modules, the foregoing actions and effects can be achieved with a simple construction.
Also, by making the end plates of material that is molded by drawing, end plates of any desired cross-sectional shape can be obtained, so end plates having the necessary strength can be obtained with a compact size, and end plates having coolant passages as described above can be formed in a simple manner.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.